The invention relates to a method and a device for controlling an output torque of an automated transmission which is coupled to an internal combustion engine.
An automated transmission is the state of the art in modern vehicles, for example commercial vehicles. By means of a transmission control unit, an automated transmission carries out, independently of the driver and under electronic control, a gear speed selection for controlling an output torque of the transmission in order to adapt a torque of the internal combustion engine, and carries out a clutch-activation operation. The transmission control unit communicates electronically with other control units of the vehicle and in this way receives the necessary input signals such as, for example, the velocity of the vehicle, engine speed, driver's request, etc., calculates itself further physical variables such as, for example, the mass of the vehicle and/or gradient of the roadway, and carries out corresponding actions for the gear speed selection. In the event of a torque request by the driver, for example, by opening the throttle, the automated transmission shifts to a relatively high transmission ratio since the internal combustion engine supplies a relatively large torque in relatively high rotational speed ranges. The relatively high rotational speed not only brings about the relatively high torque but also disadvantageously results in higher fuel consumption.
Internal combustion engines such as a piston engine of the type of a diesel engine, are equipped with an exhaust gas turbocharger for increasing an intake pressure in an intake line for the internal combustion engine. These internal combustion engines have, during acceleration and specifically at a low engine speed, an operating state which is referred to as turbo lag. Here, when the throttle is opened, the internal combustion engine does not react by increasing the engine speed until after a specific time delay in which there is no exhaust gas energy available for driving the exhaust gas turbocharger and therefore no compressed intake air available at a corresponding intake pressure.
German patent document DE 103 61 913 A1 specifies a method of providing charge resistance with compressed air from a buffer accumulator for turbo lag in an internal combustion engine with an exhaust gas turbo-charger. This additional air is fed to the internal combustion engine downstream of the exhaust gas turbocharger in the direction of flow, via a control valve during operation in a rotational speed range with an inadequate torque. The control valve is controlled here by a regulator which receives pulses from the accelerator pedal and a rev counter.
EP 12 55 031 A2 describes a control system and a method for a vehicle having an internal combustion engine with a turbocharger and a transmission. The engine is controlled by an engine control unit, and the transmission is controlled by a transmission control unit. These control units communicate with one another. The internal combustion engine is equipped with an exhaust gas recirculation means and an associated valve. The exhaust gas recirculation means has a cooler. An air blower device for blowing in compressed air is not specified.
In order to get around the turbo lag, solutions have been proposed which are described, for example, in laid-open patent applications DE 10 2006 008 783 A1, DE 10 2006 008 785 A1 and WO 2006/089779 A1. An internal combustion engine with turbocharger has an air blower device for compressed air. Here, the air blower device is used to blow in compressed air, for example from a compressed air accumulator, in a controlled fashion into the intake line, specifically into the inlet manifold, of the internal combustion engine, in order to cover the intake air demand of the internal combustion engine when said demand increases. This specified device and this specified method have the object of improving the acceleration behavior of the commercial vehicle with a turbocharged piston internal combustion engine, i.e. of increasing the acceleration capability.
The object of the present invention is to make available a method and a device for controlling an output torque of an automated transmission which is coupled to an internal combustion engine while taking into account operating parameters of the internal combustion engine and of the automated transmission, in which case the above disadvantages are significantly reduced and further advantages are provided.
The object is achieved with a method and device for controlling an output torque of an automated transmission which is coupled to an internal combustion engine and has a transmission control unit, wherein the internal combustion engine has an exhaust gas turbocharger and an air blower device for blowing air into an intake line. A torque request is received by the transmission control unit, which generates an air blowing-in signal on the basis of the torque request and current operating parameters of the internal combustion engine and of the automated transmission. The output torque is controlled by activating the air blower device on the basis of the air blowing-in signal in order to blow air into the intake line of the internal combustion engine for a definable time period.
When there is a torque request and on the basis of current operating parameters of the internal combustion engine and of the automated transmission, a transmission control unit generates an air blowing-in signal which activates the air blower device for a definable time period. As a result, advantageous control of an output torque of the automated transmission is achieved in that, for example, shifting processes for increasing the output torque are reduced in frequency or avoided, as a result of which there is a saving in fuel since the internal combustion engine maintains its rotational speed which is favorable in terms of consumption, but its torque is increased by the blown-in air.
A shifting strategy of the transmission control unit of an automated transmission for shifting gear speeds and for controlling the clutch can be advantageously adapted to these possibilities of a rapid increase in torque and expanded torque range of a turbocharged internal combustion engine. In this context, the blowing-in process which is initiated by the air blowing-in signal is selectively integrated into the shifting strategy of the transmission, i.e. the transmission control unit activates the air blower device in such a way that air is blown in in accordance with the air blowing-in control signal. In this context it may also be possible for the air blowing-in control signal to define, for example, the duration, pressure and/or quantity of blowing-in air through its shape and/or chronological length.
The transmission control unit is connected to an air blowing-in control unit. Of course, the transmission control unit can be part of an engine control unit. It is also possible for the air blowing-in control unit to be a component of the transmission control unit and/or engine control unit.
A method according to the invention for controlling an output torque of an automated transmission which is coupled to an internal combustion engine and has a transmission control unit, wherein the internal combustion engine has an exhaust gas turbocharger and an air blower device for blowing air into an intake line, includes the following method steps:
(a) reception of a torque request by the transmission control unit;
(b) generation of an air blowing-in signal by the transmission control unit on the basis of the torque request and current operating parameters of the internal combustion engine and of the automated transmission; and
(c) control of the output torque by activating the air blower device on the basis of the air blowing-in signal in order to blow air into the intake line of the internal combustion engine for a definable time period.
A device according to the invention for controlling an output torque of an automated transmission having a transmission control unit, which transmission is coupled to an internal combustion engine having an exhaust gas turbocharger, includes:
(a) an engine control unit for controlling the internal combustion engine and generating and/or passing on torque requests for the transmission control unit; and
(b) an air blower device having an air blowing-in feed section with an air blowing-in control unit for the controlled feeding of blowing-in air into an intake line of the internal combustion engine, wherein the transmission control unit is designed to generate an air blowing-in signal on the basis of the torque request and current operating parameters of the internal combustion engine and of the automated transmission, and wherein the transmission control unit is connected to the air blowing-in control unit in order to control the output torque.
Such integration of the blowing-in process for air, for example compressed air, from a reservoir or compressed air vessel, into a switching strategy of the automated transmission allows an advantageous saving in fuel in that shifting processes for increasing the output torque are reduced or avoided. The shifting processes normally assume a relatively high transmission ratio (for example when there is a torque request above what is referred to as a kick down) since the internal combustion engine has a relatively high torque at relatively high rotational speed ranges. However, the relatively high rotational speed also means relatively high fuel consumption. In the event of a torque request and current operating parameters of the internal combustion engine and of the automated transmission, according to the invention an air blowing-in signal is generated which causes air to be blown into the intake line of the internal combustion engine, as a result of which the torque of the internal combustion engine is increased while the rotational speed essentially stays the same and therefore a rotational speed which is favorable in terms of consumption is maintained. A shifting process to a relatively high transmission ratio is not necessary or can take place in a delayed fashion, for example after the blowing-in process has ended.
The current operating parameters of the internal combustion engine may be, for example, its rotational speed, temperature, load, and torque. Current operating parameters of the automated transmission are, for example, the selected gear speed, the shifting process, the clutch operation process, the intermediate throttle-opening process, the intermediate clutch operation process, and the like.
In certain cases it may also be advantageous that switching to another transmission ratio occurs after a delay during the blowing-in process or occurs together with it.
In addition to such avoidance of shifting processes to relatively high transmission ratios, a switching point at which the transmission performs the shifting process to a relatively low gear speed can be adjusted in the direction of relatively low rotational speeds of the internal combustion engine, since with the blowing-in process when the output torque is controlled a shifting process of the automated transmission to a relatively low transmission stage occurs on the basis of a torque request for decreasing the torque after the activation of the air blower device has ended, and in this context a relatively large engine torque, i.e. torque of the internal combustion engine, is present.
Furthermore, it may also be possible that the transmission shifts into a relatively high gear speed earlier during acceleration processes, that is to say together with the blowing-in process or during the blowing-in process, and therefore avoids phases of a high engine speed which correspond to relatively high fuel consumption. This is because after the shifting process a possible lack of sufficient engine torque can be compensated by selectively blowing in air.
It is also possible for one or more gear speeds to be bypassed when shifting up or shifting down.
The air blowing-in signal can be generated on the basis of the torque request and current operating parameters of the internal combustion engine and of the automated transmission, which is carried out, for example, by the transmission control unit in which the shifting strategy can be present, for example as software of a microcontroller system. The air blowing-in signal can therefore be advantageously adapted in a flexible way to operating conditions.
The transmission control unit is preferably connected to an engine control unit or another control unit of the internal combustion engine for communicating in order to receive torque requests and current operating parameters of the internal combustion engine. In this context, the other control units can have the following devices for generating a change in torque: automatic cruise controller; electronic stability controller; traction controller; driver assistance systems, and the like.
In a further embodiment, when an air blowing-in signal is generated, operating parameters of the exhaust gas turbocharger such as, for example, rotational speed, delivery capacity and/or compressor pressure are taken into account. It is possible here for the rotational speed of the turbocharger to be measured by way of a rotational speed sensor which is connected, for example, to the transmission control unit. The delivery quantity of the turbocharger can also be calculated from various input signals, for example of the engine control unit, by the transmission control unit. Likewise, a compressor pressure can be determined by use of a sensor which also communicates with the transmission control unit.
This is advantageous, for example, if when travelling at a constant speed and with a medium rotational speed of the internal combustion engine, an acute torque request is made by the driver. In this context, when the delivery quantity of the exhaust gas turbocharger is known the transmission control unit can detect whether the compressor pressure of the exhaust gas turbocharger is sufficient and, if appropriate when the compressor pressure is not sufficient, it can accelerate the build-up of compressor pressure by correspondingly blowing in air. This avoids the situation in which only what is referred to as shifting down enables the transmission to meet the driver's request to increase the torque and this brings about increased fuel consumption.
The definable time period for the blowing in of air can be defined by an operating parameter of the air blowing-in signal. It is therefore possible, for example, to define, and also change, the blowing-in process by use of a chronological length of the air blowing-in signal. It is also possible for the definable time period to be switched on by the air blowing-in signal in the form of a starting pulse and to be switched off in the form of a stop pulse. Pulse sequences, for example with a variable frequency, are also possible. In this context it is decisive that the air blowing-in signal has a high degree of immunity to faults.
It is known that an unsynchronized manual shift transmission in a heavy commercial vehicle is shifted up by double activation of the clutch (referred to as “double declutching”) and shifted down by what is referred to as “double declutching with opening of the throttle”. The shifting method in a commercial vehicle which is equipped with an automated and unsynchronized step-by-step variable-speed transmission has a similar method sequence to that carried out by the driver during manual shifting.
A significant advantage of an automated step-by-step variable-speed transmission consists in the fact that the shifting is carried out in a shorter time than is required for manual shifting by a driver. This results in a shorter time with a loss of traction force compared to a manual shift transmission. There are commercial vehicles, for example in the construction industry, in which it is highly significant that the vehicle operates with a loss of traction force for as short a time as possible. This automated shifting process contains a plurality of method steps, one of which is “double declutching with opening of the throttle”, as a result of which the piston internal combustion engine is briefly accelerated in order to reach the required rotational speed for synchronizing the gear stages. The input shaft of the transmission can then be accelerated by briefly closing the clutch at the synchronous speed. During shifting up, double declutching occurs without opening the throttle. The greatest amount of time required for this double declutching process with opening of the throttle is the acceleration of the internal combustion engine since an engine of a turbocharged design can be operated only at very low charge pressures in this operating state. This results in a similar torque to that of an induction engine. This acceleration can be improved significantly in that, in this intermediate throttle-opening phase, the air blowing-in signal is generated for a definable time period and blowing-in air is blown in, as a result of which the rotational speed of the engine is increased at a higher charge pressure. This intermediate throttle-opening phase can therefore be reduced by approximately 50 to 70%.
The response behavior plays a significant role when a vehicle with a turbocharged internal combustion engine is accelerated out of a stationary state. In the case of a poor response behavior (for example on a positive gradient of a roadway) the driver will attempt to implement a sufficiently large traction force by means of high rotational speeds and a correspondingly high clutch slip. This results in high loading of the components with a high degree of wear of the clutch lining, for example a burnt clutch lining. In a further design there is then provision for the air blowing-in signal to be generated for a definable time period during a starting process. This triggers selective blowing-in of compressed air, as a result of which the required engine speed during the acceleration process of a turbocharged internal combustion engine out of the stationary state is kept at a significantly lower level than it would be without it. However, this requires the activation of the clutch to be adapted. This results in a relatively short clutch operation phase and improved gradient-climbing capacity. At the same time, the loading on the components is reduced significantly and the service life of the clutch is increased.
In one preferred embodiment there is provision for the air blowing-in feed section to be a fresh gas line section of a device for supplying fresh air for the controlled blowing in of compressed air.
By applying the method described above, the internal combustion engine is able to cover effectively an extended engine speed range. This permits the gear speed of the transmission or transmissions used to be reduced, which saves costs and reduces the amount of installation space required for the transmission. At the same time, this results in a reduction in weight with associated reduced consumption of fuel.
It is contemplated that the air blower device has a separate control unit for controlling it or that it is controlled by the engine control unit or the transmission control unit or some other control unit of a vehicle which performs at least one further control task and which is also designed for controlling the air blower device. The functional linking which is provided according to the claims is essential.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.